Apparatus for vacuum treating liquid steel according to the circulation method



V 8, 1969 w. COUPETTE APPARATUS FOR VACUUM TREATING LIQUID STEEL:

ACCORDING To THE CIRCULATION METHOD Filed June 27, 1966 highly heated 9A ciPcu/ating gas United States Patent 4,067 Int. Cl. C21c 7/10; B0117/00 US. Cl. 266-34 3 Claims ABSTRACT OF THE DISCLOSURE A degasifyingvessel with two pipes extending into molten metal, especially steelmelt, for vacuum treating according to the circulating degasifyingmethod. Metallurgical reaction is made more versatile and intensive byproviding the degasifying vessel with at least one adjustable plasmaburner for blowing in a highly heated reactive gas able to flow aroundmolten metal droplets due to splashing in the vessel. Heat energy ofmulti-atom inert gases is extremely high since the specific heat due tothe increase in temperature is increased by dissociation and ionizationenergy; due to high temperatures at the phase borders, an intensive andquick reaction of the metal droplets is obtained. Heat losses occurringduring the vacuum treatment are simultaneously obviated by radiation ofthe high temperatures, very favorable in a vacuum.

The present invention relates to an apparatus for vacuum treating liquidsteel according to the circulating method, in which a degasifying vesselwith two pipes extends into the steel melt. Devices of this general typefor carrying out the circulating degasifying method are known. In orderto induce the chemical reaction, it is known instead of conveyor gas toconvey inert or reactive gases into the riser.

It is also known to carry out an inductive heating or a heating by meansof a graphite rod in the interior of the degasifying vessel. Theseheretofore known devices, however, have the drawback that the method isdifficult to carry out and involves considerable costs for the heating.

It is, therefore, an object of the present invention to make themetallurgical reaction more versatile and intensive than heretoforepossible while permitting the employment of heretofore known degasifyingvessels.

It is still another object of this invention to provide a device forvacuum treating liquid steel according to the circulating method, whichwill be relatively simple in construction and easy to handle.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawing diagrammatically illustrating a device according tothe invention for vacuum treating liquid steel.

The problem underlying the present invention has been solved byproviding the degasifying vessel with one or more adjustable plasmaburners for blowing in a highly heated gas. Modern plasma burners have apower of many thousand kilowatt and are able to produce gas temperaturesup to 50,000 C. Such plasma burner or burners are arranged at the upperportion of the degasifying vessel so that hot gases conveyed from saidburner or burners into the vessel almost flow only around the steelwhich splashes in the vessel. For purposes of degasification, smalldroplets down to 0.5 millimeter are very much desired in the vacuumchamber. However, they have the drawback that they cool off too quicklyand thus give 06:

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less gas and react in a poor manner. This drawback will be overcomewhen, in conformity with the present invention, the hot gases are ableto flow around the said droplets.

Plasma burners are operated by means of inert gas, such as argon, or areactive gas, as for instance, hydrogen, oxygen, methane, carbontetrachloride, chlorine, sodium vapor, or the like, or mixtures thereof.The heat energy,

especially of the multi-atom gases, is extremely high since the specificheat due to the increase in temperature is increased by the dissociationand ionization energy. In view of the obtained high temperatures at thephase borders, an intensive and quick reaction of the steel droplets isobtained.

The heat losses occuring during the vacuum treatment are at the sametime obviated according to the present invention, namely by theradiation of the high temperatures, which radiation is very favorable ina vacuum.

Referring now more specifically to the drawing representing a sectionthrough a degasifying vessel, the degasifying vessel 1 is in a mannerknown per se with its two pipes 2 and 3 immersed into a ladle (notillustrated) which is filled with liquid steel. By means of a conduit 4communicating with the riser 2, argon or any other suitable gas is blowninto the vessel 1 whereby in a manner known per se a circulation will beobtained. In the degasifying vessel 1, the steel is pulled upwardly andtorn into droplets. Vessel 1 communicates with the vacuum pump through aconnection 5 and a hose (not illustrated) which is connected toconnection 5.

In conformity with the present invention, the degasifying vessel 1 isequipped with controllable plasma burners 6 arranged in the upperportion of vessel 1. Burners 6 are operated by an inert gas, or areactive gas, so that the highly heated gas will be able to flow aroundthe steel droplets. With a ton melt to be degasified, burners with apower of from 1000 to 2000 kilowatts will suflice. In order notunnecessarily to place the vacuum pumps under load, high gastemperatures are selected so that a high heat supply with a relativelysmall quantity of gas with a temperature of approximately 25,000 C. willbe obtained. Advantageously, the supplied quantity of gas should notexceed 10% of the output of the vacuum pumps.

When employing hydrogen for deoxidizing disquiet steels, water steam isformed which with steam jet ejectors does not place a material load onthe pump system, because water steam deposits in the condensator. It isimportant for the metallurgical reaction that gaseous products only formwhich cannot impurify the steel. Furthermore, it is advantageous for thevacuum gas metallurgy that all reaction products are immediatelywithdrawn at the border layers so that they cannot act against eachother. Thus, with the device according to the present invention, it ispossible to carry reactions of various types without the necessity ofemploying the greatly interfering metallurgical slags.

When employing a plasma burner, it is also possible to keep thedegasifying vessel warm during treatment intermissions. This isparticularly advantageous with a high grade lining because such liningsare sensitive to temperature changes.

Plasma burners are generally Well known and have been described, forinstance, in French Patent 1,311,252 which issued on Oct. 29, 1962. Thepower output of such plasma burners may be controlled in any convenientmanner, for instance, by alternating current or three-phase current.This is particularly favorable when a plurality of such burners areemployed since" with superposition of three-phase current the power ofthe burners may be increased to a maximum in a very simple manner, whichis practicallynot possible with methods not employing superposition ofthree-phase current.

The control of such plasma burners is likewise well known and, forinstance, described and illustrated in said French patent. A controlcircuit of this type is diagrammatically illustrated in the presentdrawing in which reference numerals 7 and 8 designate direct currentgenerators respectively conductively connected to the electrodes 9, 10and 11, 12 of the two burners 6 shown in the drawing. There is,furthermore, provided a source 13 of threephase current, the three-phase14, 15, and 16 of which are respectively connected to electrodes 10 12and a further electrode of a further burner (not shown).

It is, of course, to be understood that the present invention is, by nomeans, limited to the particular arrangement shown in the drawing butalso comprises any modifications within the scope of the appendedclaims. Thus, while according to the drawing the degasiiying vessel isequipped with a plurality of plasma burners, it is to be understood thatthe arrangement would also operate properly with one burner only.

What I claim is:

1. An apparatus for vacuum treating liquid steel according to thecirculation method for degasifying the steel, comprising a degasifyingvessel, pipe means connected to the lower portion of said vessel andcommunicating with the interior thereof, said pipe means being immersedin a steel melt, conduit means communicating with said pipe meansthrough which gas is admitted for withdrawing steel from the steelmeltand throwingtthe same in form of droplets into said degasifyingvessel, adjustable plasma burner means arranged at the upper portion ofsaid vessel and operable by inert or reactive gas to convey highlyheated gases into the interior of said vessel and around steel dropletsthrown up into the flow of said highly heated gases, and vacuum creatingmeans connected to and communicating with said degasifying vessel.

2. An apparatus according to claim 1, in which means for conveyinghigh-heat gas is associated with said plasma burner which means isoperable to furnish a small quantity of said gas at a temperature around25,000 C.

3. An apparatus according to claim 1, in which a plurality of plasmaburner means are associated with said degasifying vessel and arranged tosupply hot gas flow around the droplets for intensive metallurgicaltreatment.

References Cited UNITED STATES PATENTS 3,147,330 9/1964 Gage 219-121 XR3,320,053 5/1967 Lehman 7549 XR 3,342,250 9/1967 Treppschuh 7549 XR L.DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner U.S.Cl. X.R.

